A tax partner finishes researching a complex ruling for a client. Work that used to take a senior associate four or five hours now takes 11 minutes. She sends the answer to the client, then looks at her timesheet and stops.
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Most people will frame this as a billing problem. No adjustment to an invoice format addresses a relationship that has quietly shifted beneath it.
The “hour” was a workaround that became the whole system
Reginald Heber Smith introduced systematic timekeeping at Hale and Dorr in the 1920s for internal management reasons, which included matter economics, partner accountability and productivity measurement. Before that, clients did not pay by the hour. Hourly billing spread through law firms across the 1960s and became dominant by the late 1970s, accelerated by Supreme Court decisions that dismantled bar association fee schedules. Accounting firms followed. The model took hold because it answered a question clients had no other way to answer: Was this advisor working hard on my problem?
You could not always audit the research or evaluate whether a memo was excellent or merely adequate, but you could count the hours and decide whether the total seemed reasonable. Time was legible to both sides in a way that expertise was not.
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“Value-based pricing” had been preached for decades without dislodging it. The alternative felt more subjective, less verifiable, harder to defend to clients who had grown accustomed to counting hours.
The hour survived because it worked, answering a real question about trust that nothing else resolved as cleanly.
What AI does that prior technology didn’t
Every wave of technology before this one made practitioners more productive without making the process visible to clients. Westlaw replaced the library, email replaced the fax, and tax software accelerated the math. Each time, firms absorbed the efficiency, kept billing by the hour, and clients had no basis to push back. They still could not see inside the work, and the opacity that made hourly billing tolerable held.
When a client knows that AI tools can research a complex ruling in minutes, a four-hour line item on the invoice signals that something in the arrangement has shifted.
Many corporate clients are already running AI tools inside their own organizations.
Steelman the defenders, then take them apart
The firms holding onto hourly billing generally offer one of three arguments.
1. Budget predictability: Clients want hourly billing because it gives them cost caps and estimates they can plan around. A client who cannot know upfront what a matter will cost has less certainty under hourly billing than under a fixed engagement fee. PwC’s US tax leader Krishnan Chandrasekhar has
2. Matter complexity: Sophisticated tax work resists scoping because the problem changes as you work through it. Most complex matters decompose into two layers: routine research and drafting, which AI has made fast and cheap, and judgment-heavy analysis, which remains hard to predict. The scoping problem has shrunk considerably for the portion of the work AI now handles.
3. Risk transfer: Value pricing moves performance risk from the client to the firm, and firms are not structured to absorb it. Proponents of this view argue that hourly billing protects firms from unpredictable matter complexity. That argument held more force when estimating the cost of routine work was genuinely difficult. Firms with serious AI capability are now far better at predicting that cost than they were five years ago, which changes the risk calculation considerably.
Beyond value-based pricing: the case for bifurcation
“Value-based pricing” has been the profession’s answer to hourly billing’s problems for 30 years, with modest results. The market data now suggests something more fundamental is happening. Among small accounting firms surveyed by
Firms getting ahead of this are splitting their work into two tracks and pricing each differently.
Routine deliverables get productized: fixed fee per memo, subscription access for ongoing research, outcome pricing on filings and compliance work. The efficiency AI has brought to this work makes it possible to price it as a product rather than a process. The margins on productized work can hold or improve because the underlying costs have fallen faster than a sensible fixed price would.
Judgment-heavy work gets repriced upward and scoped around the client’s question rather than the hours required to answer it: retainers for ongoing advisory relationships, decision-support engagements, success fees on transactions where the outcome is clear. This work has always been the most valuable thing a tax advisor does, but the billable hour made it hard to price separately, because research hours blurred together with advisory judgment on the same invoice.
Firms running both tracks are redirecting capacity recovered from routine work toward the advisory relationships that actually warrant senior expertise. While those who are preserving hourly billing across the board are watching realization compress on routine work and losing advisory engagements to competitors who scope it differently.
The new trust contract has four explicit terms
The old trust contract was that the client trusted the process by counting hours as a proxy for effort and expertise. What replaces it now is an explicit conversation about what the engagement actually covers, one that the billable hour was specifically designed to make unnecessary.
The firms moving fastest right now are rewriting their engagement letters around four terms.
1. Scope: What is being delivered, and by when.
2. Method: Which work is AI-assisted and which requires human judgment, disclosed rather than assumed.
3. Deliverable: The output the client can evaluate, not the effort that produced it.
4. Accountability: The firm’s judgment on the line, not the time spent reaching it.
Rewriting engagement terms along these lines is harder than adjusting a rate. It means talking with clients about how the work actually gets done, a conversation the billable hour was specifically designed to avoid. Clients who already know AI exists will have that conversation regardless. The question for any firm is whether to define its terms before the client does.
What’s at stake
The decision in front of every firm isn’t whether to change pricing. It’s whether to be the firm that defined the new contract for the client, or the firm that had it defined for them.
The billable hour was always just a stand-in for something harder to measure. AI has finally made that obvious.
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